Controller and Form

Question

What's the key difference between:

amazing_forms_contribute:
  path: 'amazing-forms/contribute'
  defaults:
    **_form: '\Drupal\amazing_forms\Form\ContributeForm'**
    _title: 'Conribute page'
  requirements:
    _permission: 'access content'

and

amazing_forms_contribute:
  path: 'amazing-forms/contribute'
  defaults:
    _**controller: '\Drupal\amazing_forms\Controller\ContributeForm::content'
link_id: 'arm.admin_product_variants_create'**
    _title: 'Conribute page'
  requirements:
    _permission: 'access content'

When I should use a controller? And when I should use a form?

Can I combine both (use controller and form)?

What is their limitation?

Answer 1

_form: We use this explicitly when one expects a classname implementing FormInterface.

_controller:It is used when one needs to return a renderable array or an object. Hence, here we call a method from its class (classname::method)

And NO you cannot use _form and _controller at the same time under defaults: since one routing only provides one functionality at a time.

See here to understand how the structure of routes are used and why they were used.Also see routing api for a more detailed understanding.